In the conventional electrochemical method determining hydrogen content in iron and steel, a thin palladium layer is electrodeposited on the one side of specimen in order to prevent the passivation of steel and to promote ionization reaction of hydrogen. However, it is very difficult to obtain a uniform deposition layer of palladium and the undeposited or bare part of the surface requires the passivation current of order of 1-2μa/cm², reducing the accuracy of hydrogen measurement. Nickel deposition was found to be much advantageous and its passivation current was less than 0.1μa/cm². The suitable thickness of electrodeposited nickel was 500-1000Å. The range of electrode potential for ionizing hydrogen was found to be -0.1-0.3 volt vs. SCE in 1N NaOH solution. In this potential region, the surface of electrodeposited nickel layer is probably covered by Ni₃O₄ or Ni₂O₃ through which however hydrogen atoms can permeate.